Lumbar spine kines

Lumbar Spine Structure and Function

• The lumbar vertebrae are notably larger than the cervical and thoracic vertebrae.
• Their primary focus is weight-bearing and transitioning forces between the axial and the appendicular skeleton. This involves transmitting force from the spine to the pelvis and the legs, as well as vice versa.
• The lumbar spine is considered triaxial, meaning it allows for movement in three planes.

Joint Types and Characteristics

• The spine contains two technical types of joints, which is especially relevant in the lumbar region due to its weight-bearing function:
  • Synovial Joints: These are the facet joints, also known as apophyseal joints, zygapophyseal joints, or z-joints.
  • Cartilaginous Joints: These are the intervertebral discs.

Facet Joints (Zygapophyseal Joints)

• These joints are mostly oriented in the sagittal plane.
• The facets are aligned at an angle of approximately $90^{\circ}$.
• They are synovial joints featuring cartilage and a joint capsule.
• Articular Orientation: The superior facet of the inferior vertebrae articulates with the inferior process of the superior vertebrae.
• Superior Facet: Oriented laterally, facing medially and slightly posteriorly.
• Inferior Facet: Faces laterally to match the superior facet of the neighboring vertebrae.
• Due to their orientation, they primarily function to facilitate flexion and extension movements.

Intervertebral Discs

• Located between the vertebral bodies, forming the anterior column of the spine.
• The discs are high in height relative to those in the thoracic and cervical regions to facilitate weight-bearing and shock absorption.
• Structure:
  • Annulus Fibrosus: The tough outer layer of the disc.
  • Nucleus Pulposus: A jelly-like substance in the center.
• Function: They are responsible for handling compression and traction forces, as well as minor amounts of shearing within the spinal column.
• Disc Pathology: When forces are distributed improperly, the annulus fibrosus can wear down or weaken. This allows the nucleus pulposus to push out through the path of least resistance. This is analogous to a jelly doughnut; if pressure is applied to one side, the jelly is forced out the other way. Terms for this include herniation, extrusion, and sequestration.
• Vacuum Effect: Traction applied to the spine can create a vacuum effect, potentially sucking a protruding disc back into place. This is a primary reason for using spinal traction in clinical settings.

Ligaments of the Lumbar Spine

• Anterior Longitudinal Ligament (ALL): Sits on the front of the spinal column. It prevents excessive extension and anterior shear (the forward slipping of a vertebrae). Anterior translation is more common in the lumbar spine due to the natural lordotic curve.
• Posterior Longitudinal Ligament (PLL): Runs behind the vertebral bodies. It prevents posterior shear and excessive flexion.
• Ligamentum Flavum: Located posteriorly; limits excessive flexion.
• Supraspinous Ligament: Located posteriorly; limits excessive flexion.
• Interspinous Ligaments: Located posteriorly; limits excessive flexion.
• Intertransverse Ligament: Located between the transverse processes. It is the primary ligament responsible for limiting lateral flexion.

Range of Motion and Limitations

Normative Values (Measured by Inclinometer)

• Flexion: $40$ to $50^{\circ}$.
• Extension: $20$ to $25^{\circ}$.
• Lateral Flexion: $25$ to $30^{\circ}$.

Factors Limiting Movement

• Flexion Limits: Restricted by posterior structures including the supraspinous ligament, posterior longitudinal ligament, ligamentum flavum, interspinous ligaments, and the erector spinae muscle group. Tightness in the facet joint capsules or the development of anterior osteophytes (spurring) due to prolonged flexed postures can also limit mobility.
• Extension Limits: Restricted by the anterior longitudinal ligament, spinous processes (bony block), and the facet joints. Arthritis or spurring in the facet joints can make extension painful and limited.
• Lateral Flexion Limits: Restricted by the intertransverse ligaments and side-bending muscles such as the Quadratus Lumborum (QL) and the contralateral erector spinae.

Arthrokinematics and Coupled Motion

Flexion and Extension

• Flexion: Facet joints perform an opening movement. The inferior facets move superiorly and anteriorly.
• Extension: Facet joints perform a closing movement. The inferior facets move posteriorly and inferiorly.

Lateral Flexion

• Side-bending involves a closing motion on the ipsilateral side (the side you are leaning toward) and an opening motion on the contralateral side.
• Closing Side: Facets move posteriorly and inferiorly (similar to extension).
• Opening Side: Facets move anteriorly and superiorly (similar to flexion).

Coupled Motion

• In the lumbar and thoracic spine (and upper cervical spine), lateral flexion and rotation are coupled in opposite directions.
• Rule: Right lateral flexion is coupled with left rotation; left rotation is coupled with right lateral flexion.
• This contrasts with the middle and lower cervical spine ($C2$ to $C7$), where coupling occurs in the same direction.

The Pelvic Girdle

• Components: The pelvic girdle includes the pelvis (two innominates), the sacrum, and the coccyx.
• Innominate Bones: Each is a fusion of the ilium, ischium, and pubis.
• Joints of the Pelvis:
  • Two Sacroiliac (SI) Joints: The junctions between the sacrum and the ilia.
  • One Pubic Symphysis: Located in the middle of the anterior portion of the pelvis.
• Functions:
  • Bony protection for pelvic organs.
  • Muscle attachment site.
  • Passage for gastrointestinal and genitourinary tracts.
  • Responsible for childbirth.
  • Weight transfer between the trunk and lower extremities.

Sacral Movements (Nutation and Counternutation)

• Nutation (Sacral Flexion): The sacral base (top) moves anteriorly and inferiorly, while the sacral apex (bottom) moves posteriorly and superiorly.
• Counternutation (Sacral Extension): The sacral base moves posteriorly and superiorly, while the apex moves anteriorly and inferiorly.
• Sacral Rotation: The sacrum can rotate between $1$ and $8^{\circ}$. Sources vary, but the joint is meant to be highly stable and robust.
• Stability and Pregnancy: During pregnancy, the hormone relaxin causes pelvic ligaments to become lax, which can lead to SI joint pain, pubic symphysis pain, and shearing. This laxity also often causes women's feet to increase by one shoe size permanently.

Pelvic Alignment and Dysfunctions

Neutral Alignment

• Iliac crests should be level.
• The Anterior Superior Iliac Spine (ASIS) and the pubic symphysis should be in the same frontal plane when standing.
• The ASIS and Posterior Superior Iliac Spine (PSIS) should be relatively level, though it is normal for the ASIS to be $5$ to $10^{\circ}$ inferior to the PSIS.

Common Deviations and Tilts

• Anterior Pelvic Tilt: The superior aspect of the pelvis tilts forward. The ASIS moves in front of the pubic symphysis and becomes more inferior to the PSIS. This is associated with increased lumbar lordosis. Imagine a bowl of punch spilling out the front.
• Posterior Pelvic Tilt: The superior aspect of the pelvis tilts backward. The ASIS moves behind the pubic symphysis and rises higher. Imagine the punch spilling out the back. Older patients with arthritis often use a posterior tilt to "gap" the spinal segments for pain relief.
• Lateral Tilt (Drop): One iliac crest is lower than the other. The condition is named for the lower side (e.g., a "right lateral tilt" means the right side is lower). This often occurs dynamically during gait if hip stability is poor.
• Pelvic Elevation (Hiking): One side of the pelvis is pulled higher than the other through concentric muscle contraction (e.g., hiking the hip to clear the floor during walking).
• Pelvic Rotation: Occurs in the transverse plane where one side is more forward than the other. It is named for the forward side. This is a normal component of gait but is considered a dysfunction if the pelvis is "stuck" in rotation.

The Lumbosacral Joint

• Definition: The junction between the fifth lumbar vertebrae ($L5$) and the sacrum.
• Anatomic Variation: Approximately $3$ to $10\%$ of the population has a sixth lumbar vertebrae ($L6$).
• Lumbosacral Angle: Unlike other block-shaped lumbar vertebrae, $L5$ is wedge-shaped. This creates a lumbosacral angle of $30$ to $40^{\circ}$ relative to the horizontal plane.
• Function: This angle automatically creates a physical lordosis at the junction.
• Clinical Significance: This is one of the most common sites for spinal wear and tear, degeneration, and lumbar fusion surgeries.

Questions & Discussion

Question: Regarding the occipital or the $C0-C1$ joint, what movement is primarily from that joint? Response: Flexion and extension.

Question: How about the $C1-C2$ joint? Response: Rotation.

Question: What is the open pack position for the lumbar spine? Response: Midway between flexion and extension, which involves a tiny bit of flexion rather than being perfectly neutral.

Question: What is the closed pack position for the lumbar spine? Response: Maximum extension (bending back all the way).

Question: What is the capsular pattern for the lumbar spine? Response: Bilateral lateral flexion having a greater restriction than extension and flexion. Both sides of lateral flexion will be equally limited and more restricted than the movements of flexion and extension.